In an artificial dialysis, for example, which requires monitoring blood which is fed to a dialysis system from a living body or blood which is returned from the system to the body, it is preferred to provide a continuous monitoring. In this instance, it becomes necessary to bleed the blood from the path of dialysis so as to be fed to a monitoring unit. Since blood which is added with a reagent or the like in a monitoring unit is discarded or disposed, it is desirable for the purpose of the continuous monitoring that the blood be continuously fed to the monitoring unit at a speed of flow which is as low as possible. It is also desirable that oscillations in the pressure, in particular, a pressure of impact be minimized in order to prevent thrombus from being formed and to increase the accuracy of measurement or study. It will be appreciated that the need for a continuous feeding at a low speed of flow with reduced oscillation of pressure also exists when injecting a very small amount of medicine or assisting liquid into the living body continuously.
To meet such requirements, a roller pump has been proposed in the art in which a pressure is applied to an elastic tube by a roller which is mounted on the distal end of a rotor comprising three or four radially extending rotary arms. A finger pump is also proposed in which a plurality of pressure plates are disposed along the direction in which the elastic tube extends, with each of the pressure plates being driven to project by a cam plate which is driven for rotation by an electric motor so that an array of cam plates produces a peristaltic motion in the tube to squeeze it for feeding a fluid located therein.
With either roller pump or finger pump, a fluid being driven is withdrawn into the tube by the restoring force of the tube as a pressure is applied to the elastic tube, and this involves a limit in principle on the flow rate which can be reduced. If a tube of a smaller diameter is employed in order to provide a reduced flow rate, there occurs a greater variation in the flow rate established, as a result of dimensional error of the tube itself or errors caused when mounting the roller or pressure plates, thus resulting in a difficulty in adjusting the flow rate. In addition, as the elasticity of the tube is degraded, the flow rate being delivered will be reduced, and a variation in the flow rate is likely to occur. Also, the ability of the tube which accommodates for a pressure impact by its own resilience will be degraded.